Tracker: CHDbits
Tracker URL: http://chdbits.org
Sign-up: Invite only
Invites: Only Admins can invite at the moment
Total torrents: 32.588
Total Users: 31.896
User limit: 35.000

CHDbits is one of the best Chinese trackers with HD content. (in my opinion the best).
It's also translated in the English language, so it won't be a problem for most of the users to use this tracker.

There almost 32000 registered users, and most of them are active.
These users can find many new HD torrents every day. Different categories and HD qualities.
Seeding in this tracker is not that hard. There are MANY Free Leech torrents every day and that makes even easier for a user to maintain a good ratio.

In the forum there is also an English section.
Users can offer or request invites from other trackers there !!!

Unfortunately the invite system is closed at the moment.
Only admins can invite new users. But there are many available accounts around, and if you are lucky you can find one.
Just be careful, because email change is not possible in CHDbits. So i suggest you to purchase an account+mail, or stay away !!!